Method of testing an airbag module

ABSTRACT

The present invention relates to a method of testing an airbag module for a vehicle and, particularly, but not exclusively, to a method of testing an airbag module for a motor vehicle such as a car. A method of testing an airbag module is provided in which said module is tested for exposure to a given fluid, for example, water. The fluid exposure test ideally comprises the step of inspecting said airbag module or a swab taken therefrom by means of Atomic Absorption Spectroscopy techniques. The present invention thereby provides a testing method sufficiently rigorous to identify fluid damage potentially suffered by a previously installed airbag module during its service life.

[0001] The present invention relates to a method of testing an airbagmodule for a vehicle and, particularly, but not exclusively, to a methodof testing an airbag module for a motor vehicle such as a car.

[0002] Airbag passive restraint systems incorporating one or more airbagmodules are widely used in motor vehicles to improve passenger safetyand their design and manufacture is well understood by those skilled inthe art. Typically, an airbag module comprises three principalcomponents: a reaction can or reaction plate; an inflator or gasgenerator; and a folded airbag. These components are generally arrangedwith the gas generator located in an opening of the reaction can andsecured together with appropriate fasteners (e.g. bolts). The mouth ofthe airbag is reinforced with a metal retainer ring and located over thegas generator. The gas generator is thereby encapsulated by the reactioncan and the airbag. The fasteners used to secure the gas generator tothe reaction can generally also secure the airbag mouth.

[0003] The reaction can is the platform upon which the gas generator istraditionally mounted and is usually manufactured as a stamped steelcomponent capable of resisting the significant forces generated duringactivation of the restraint system. Reaction cans are however beingincreasingly manufactured from molded plastics materials such as glassfilled nylon. The gas generator is typically provided as a metal bodywhich houses a suitable igniter, a gas generant and, depending on thegas generant used, appropriate filters. The person skilled in the artwill be familiar with various different types of gas generator presentlyused in airbag modules. The body of the gas generator is generallyprovided with a plurality of exit ports for permitting the release ofinflation gas to the airbag. The airbag itself is folded adjacent thegas generator so as to be readily inflatable upon system activation.

[0004] In addition to the aforementioned principal components, an airbagmodule also incorporates an electric circuit for enabling electricalconnection of the module to control circuitry of the associatedrestraint system. The circuit typically includes an electric igniterwith an integral connector or set of lead wires for connection to thevehicle wiring harness. An airbag module also traditionally incorporatesan airbag cover or door which encloses, retains and protects the airbagin its folded position until activation of the restraint system. Thecover or door is configured to split along a tear seam when the airbagis inflated.

[0005] An airbag module provided in a motor vehicle such as a car iscommonly mounted in a hidden compartment within, for example, thevehicle dashboard or steering wheel. In the event of the motor vehicleundergoing a predetermined deceleration (of a magnitude usually onlygenerated during a vehicle collision), the control circuitry associatedwith the airbag module applies an activation signal to the electricigniter circuit so as to activate the module's gas generator. Inresponse to the activation signal, the igniter fires, which, in turn,ignites the gas generant. The gas generant then rapidly produces highpressure inflation gas.

[0006] The inflation gas produced by the gas generant rapidly progressesfrom the body of the gas generator via the exit ports and flows into theopen mouth of the folded airbag. This causes the airbag to expand anddisplace any associated airbag cover and vehicle fascia. Where the gasgenerator uses a solid gas generant, the inflation gas is first directedthrough filters. This cools the gas and removes any burning particlestherefrom which may damage the airbag or cause injury to a passenger.Once deployed, the inflated airbag provides a cushion for restrainingand absorbing the kinetic energy of a passenger. An airbag passiverestraint system is thereby capable of increasing the safety of vehiclepassengers.

[0007] For many years it has been common practice to recycle certaincomponents of end-of-life motor vehicles. A wide range of componentssuch as engine blocks, exhaust pipes and brake discs have been madeavailable by breakers as relatively inexpensive and generally reliablespare parts. This provision of spare parts not only provides consumerswith an attractive alternative to purchasing new components(particularly in circumstances where the vehicle under repair isrelatively old), but also has a beneficial effect on the environmentthrough reducing waste. Indeed, in this latter regard, legislationworldwide is tending to increasingly require vehicle manufacturers toincrease the proportion of vehicle components which may be recycled.Although it is presently possible to recycle the vast majority ofvehicle components, constraints imposed by the technology used in airbagpassive restraint systems have, in the past, prevented the recycling ofairbag modules. If an airbag module needs to be replaced, the onlyoption hithertofore has been to fit a newly manufactured module.

[0008] Unlike many components found in a motor vehicle, a visualinspection of a previously installed airbag module is not sufficient todetermine suitability for future use. The current design of a module, asdiscussed above, is such that the airbag itself may be deployed on onlyone occasion. Although application of a suitable activation signal willallow determination of whether or not a previously installed airbagmodule is in good order, subsequent use of the module would not bepossible either because the module has failed to activate (indicatingits unsuitability for use) or because the module has been properlyactivated (rendering it unsuitable for use due to, inter alia, gasgenerant exhaustion). Accordingly, there has been no option in the pastbut to provide an airbag module as an entirely new piece of equipment.Only in this way has it been possible to effectively guarantee the safeand reliable operation of an airbag passive restraint system.

[0009] It is an object of the present invention to provide a method oftesting an airbag module.

[0010] It is a further object of the present invention to provide amethod of testing the suitability of a previously installed airbagmodule for reuse.

[0011] A first aspect of the present invention provides a method oftesting an airbag module comprising the step of testing said module forexposure to a given fluid. The given fluid may be water. A number oftests are conducted on certain components of an airbag module at certainspecific stages during module manufacture, however these tests alone arenot sufficiently rigorous to identify the damage potentially suffered bya previously installed module during its service life. The presentinvention provides for the testing of module exposure to a fluid such aswater. Any damage arising from exposure to water may not be apparentfrom a mere visual inspection or the presently used testing techniques,but may nevertheless render an airbag module inoperative or seriouslydegrade its performance capability.

[0012] The fluid exposure test may comprise the step of inspecting saidairbag module or a swab taken therefrom by means of Atomic AbsorptionSpectroscopy techniques. Also, the fluid exposure test may comprise thestep of inspecting said airbag module or a swab taken therefrom fordeposits of a metal. Preferably, the step of inspecting for deposits ofa metal comprises the step of inspecting for cations. It is desirablefor the step of inspecting for deposits of a metal to quantify theamount of metal deposited. Preferably, the amount of metal deposited isquantified for a given surface area of airbag module.

[0013] It is particularly preferable for the step of inspecting fordeposits of a metal to comprise the step of taking a swab from a surfaceof said airbag module by applying a solvent to said surface. The solventmay be 5% hydrochloric acid. Desirably, the step of inspecting fordeposits of a metal further comprises the step of agitating said swabwith 1% lanthanum chloride solution. In addition, the step of inspectingfor deposits of a metal ideally further comprises the step of inspectingthe mixture of 1% lanthanum chloride solution and swab by means ofAtomic Absorption Spectroscopy so as to determine the quantity of ametal present in said mixture.

[0014] The swab may be taken from a surface of said airbag module whichcannot be conveniently wiped clean. Said surface is ideally a surface ofthe gas generator or a surface adjacent to the gas generator. However,said surface may be a surface of the reaction can.

[0015] It is also desirable for the fluid exposure test to comprise thefurther step of determining a threshold quantity of a deposited metalwhich, if found on said airbag module, indicates an unacceptable risk ofsaid module having been damaged through fluid exposure.

[0016] The deposited metal may be calcium or sodium.

[0017] Thus, where a motor vehicle has been immersed in water (e.g. dueto flooding), a potential degradation of the vehicle's airbag module asa result of water exposure may be detected by the present invention. If,during the testing of the airbag module in accordance with the presentinvention, it is determined that the airbag module has been exposed towater (or that there is an unacceptably high risk that the module hasbeen damaged due to water exposure), then the module will not beregarded as acceptable for future use. The testing method of the presentinvention therefore represents a significant advancement in the art.

[0018] A second aspect of the present invention provides a method oftesting an airbag module comprising the steps of: (i) locating an airbagmodule which has been previously installed; (ii) establishing a set ofcriteria to be satisfied before said airbag module is deemed acceptablefor future use; and (iii) investigating against said set of criteria soas to determine the acceptability of said airbag module for future use.These steps may comprise the method of testing an airbag module forexposure to a given fluid as disclosed above.

[0019] Thus, the present invention provides means for permitting there-use of an airbag module which has been previously installed in amotor vehicle. Where a motor vehicle has reached the end of itsoperational life, the present invention provides for the investigationof an airbag module installed in said vehicle against a set of criteria.If these criteria are satisfied, then the airbag module may be regardedas acceptable for future use, even though it may not be a new piece ofequipment. The criteria to be satisfied may vary depending on the typeof airbag module in question. Also, the criteria to be satisfied may bemore stringent for old modules than for recently installed modules.

[0020] A method of testing an airbag module for a vehicle according tothe present invention will now be described with reference to theaccompanying drawings, in which;

[0021]FIG. 1 is a flow chart showing a procedure for obtaining vehicledata;

[0022]FIG. 2 is a flow chart showing a procedure for obtaining airbagmodule data;

[0023]FIG. 3 is a flow chart showing a procedure for testing an airbagmodule; and

[0024]FIG. 4 is a flow chart showing a procedure for testing an airbagmodule for fluid exposure.

[0025] A recycled airbag module may be certified as suitable for futureinstallation and use in a vehicle provided certain criteria aresatisfied. The following procedural steps determine this suitability.The general aim of the various steps is to identify undesirabledegradation of a subject airbag module, without disassembly thereof,through technical inspection/testing, and, to identify, through aninvestigation of appropriate records, any event in the history of themodule which may indicate a likelihood of undesirable degradation.

[0026] Procedural Step 1—Vehicle and Airbag Module Details:

[0027] In circumstances where the airbag module under investigation hasbeen previously installed in a motor vehicle (e.g. in a vehicle which isno longer operational, i.e. an End of Life Vehicle (ELV)), a firstprocedural step seeks to uniquely identify said vehicle and identifyevents in the history of said vehicle which may have degraded thesubject module. This is achieved through a visual inspection of officialdocuments relating to said vehicle. The following vehicle details arerecorded—

[0028] a) Vehicle original equipment manufacturer (OEM)

[0029] b) Vehicle model

[0030] c) Vehicle body style

[0031] d) Vehicle Identification Number (VTN)

[0032] e) Vehicle model year

[0033] f) Vehicle log available?—Yes/No

[0034] g) Vehicle involved in collision prior to current retirementevent?—Yes/No

[0035] If “Yes”, then collision type?—

[0036] • Front • Side • Rear • Roll Over

[0037] h) Vehicle retirement due to wear and tear?—Yes/No

[0038] If “No”, then vehicle retirement due to collision?—Yes/No

[0039] If “Yes”, then collision type?—

[0040] • Front • Side • Rear • Roll Over

[0041] If “No”, then vehicle retirement due to vandalism?—Yes/No

[0042] If “No”, then reason for vehicle retirement?

[0043] i) Vehicle ever immersed in water?—Yes/No

[0044] Having recorded the details of any vehicle (or vehicles) in whicha subject airbag module has been previously installed, the followingdetails of the airbag module itself are investigated and recorded—

[0045] j) Airbag Module manufacturer

[0046] k) Airbag Module serial number

[0047] l) Airbag Module gas generator type

[0048] m) Airbag Module date of manufacture

[0049] The date of manufacture of the airbag module is particularlyrelevant where the propellant has a limited useful life. In such cases,the date of manufacture is used to calculate the remaining life of thepropellant. An expiry date for the propellant is then indicated on afinal certification label attached to the airbag module on completion ofthe investigation procedure.

[0050] The above details are conveniently provided in response to theprompts of either dedicated electronic hardware or a personal computerexecuting appropriate software. Indeed, all procedural steps aredirected by the prompting of an operator in this way. The response toall prompts is electronically stored under a unique identificationnumber ascribed to the subject airbag module at the beginning of theinvestigation procedure. A label marked with this identification numberis then attached to the module so as to provide traceability. Theidentification label also allows ready access to the determination ofthe investigation procedure as a whole or of a particular proceduralstep. For additional convenience, the identification number is marked onthe identification label as a bar code. The identification number of aparticular airbag module may be then quickly accessed by means of a barcode reader. The identification label is preferably printed and securelyattached to the subject module at the end of the first procedural step.

[0051] Procedural Step 2—Electrical Test:

[0052] A second procedural step seeks to determine the electricalintegrity of the lead wire (if present), the electrical connector andthe igniter circuit. The procedure is conducted with suitable equipment(e.g. a Squib Circuit Tester) for measuring the resistance of a circuitin response to the accurate application of an appropriate current for aspecific duration. This electrical testing equipment is connected to thesubject module by means of the module's electrical connector. Theelectronic hardware directing the investigation procedure is adapted toindicate to the operator the adapter required for connection to themodule's electrical connector. This is achieved on the basis ofinformation supplied during the first procedural step. Thus, once thevehicle and airbag module details required by the first procedural stephave n stored under a module's identification number, the scanning ofthat module's identification label will allow convenient identificationof the required adapter. A suitable adapter is then selected from anappropriate store. The controlling electronic hardware is alsoconfigured to request confirmation from the operator that the correctadapter has been fitted. If the correct adapter is not available, thenfurther prompts directing completion of the electrical test arewithheld.

[0053] Once the correct adapter has been fitted so as to connect thesubject airbag module to the electrical testing equipment, the operatoris directed to place the module in a shielded test station. This ensuressafety in the event of the airbag module being activated. Thecontrolling electronic hardware is connected to the electrical testingequipment so as to automatically set the test parameters (on the basisof information supplied during the first procedural step), conduct theelectrical test and record the results. The test undertaken depends uponwhether or not the OEM specification for the subject module isavailable. If the OEM specification is known, then the airbag module istested to the electrical criteria defined therein. Otherwise, the airbagmodule is tested to a default set of electrical criteria which may ormay not be specifically tailored to the particular type of module underinvestigation.

[0054] Airbag Module OEM Specification Available—

[0055] A first test current is applied to the igniter circuit at thelevel defined in the OEM specification and the current resistance ismeasured.

[0056] The measured resistance is recorded and compared with therequirements of the OEM specification.

[0057] If the measured resistance does not satisfy the requirements ofthe OEM specification, then the airbag module is rejected and notsubjected to further investigation.

[0058] A “no fire” test current is applied to the igniter circuit at thelevel and for the duration defined in the OEM specification and theresponse of the airbag module is monitored.

[0059] If the airbag does not deploy, then the airbag module isconsidered to satisfy the “no fire” electrical requirements of the OEMspecification.

[0060] If the airbag does deploy, then the airbag module is rejected andnot subjected to further investigation.

[0061] Airbag Module OEM Specification Unavailable—

[0062] A test current of generally 100 mA and 200 mA is applied to theigniter circuit. The igniter bridgewire resistance, the resistance toground and the shunt resistance is measured.

[0063] The measured resistances are recorded and compared withpredetermined baseline requirements. If the measured resistances do notsatisfy the predetermined baseline requirements, then the airbag moduleis rejected and not subjected to further investigation.

[0064] The results of the electrical test are recorded under theidentification number of the subject module.

[0065] Procedural Step 3—Foreign Matter Test:

[0066] A third procedural step seeks to identify the presence of foreignmatter (e.g. grit/dirt) within the airbag module under investigation.This is achieved by means of a shake test and an X-ray test. The shaketest simply involves shaking or vibrating the subject module so that anyloose foreign matter within the module rattles in an audible manner. TheX-ray test requires the use of X-ray equipment which preferablyincorporates a conveyor belt for moving the subject module when exposedto X-rays and an appropriate shield for protecting the operator. Theelectronic hardware controlling the investigation is adapted to ask theoperator for the module's identification number and to provide theoperator with appropriate instructions for using the X-ray equipment.The identification number is typically supplied by scanning the bar codeof the module's identification label. On completion of the foreignmatter test, the controlling electronic hardware prompts the operator asfollows —

[0067] Was any foreign matter detected?—Yes/No

[0068] If “No”, then completion of the foreign matter test is confirmed.

[0069] If “Yes”, then can the foreign matter be removed without damageto the airbag module?—Yes/No

[0070] If “Yes”, then completion of the foreign matter test is confirmedsubject to removal of the identified foreign matter from the airbagmodule.

[0071] If “No”, then the airbag module is rejected and not subjected tofurther investigation.

[0072] The results of the foreign matter test are recorded under theidentification number of the subject module.

[0073] Procedural Step 4—Fastener Integrity Test:

[0074] A fourth procedural step seeks to confirm that all fasteners(e.g. screws, rivets and bolts) of the airbag module are in place andsecure. This is achieved through visual inspection. The electronichardware controlling the investigation is adapted to ask the operatorfor the module's identification number and to provide the operator withappropriate instructions for completing the fastener integrity test. Theidentification number is typically supplied by scanning the bar code ofthe module's identification label. On completion of the test, thecontrolling electronic hardware prompts the operator as follows —

[0075] Were all fasteners in place and secure?—Yes/No

[0076] If “Yes”, then completion of the fastener integrity test isconfirmed.

[0077] If “No”, then the airbag module is rejected and not subjected tofurther investigation.

[0078] The results of the fastener test are recorded under theidentification number of the subject module. Optionally, photographs ofthe fasteners may be taken and digitally stored under the module'sidentification number. The direction of the controlling electronichardware is such that the subject module is rejected if merely one ofits fasteners is loose or missing.

[0079] Procedural Step 5—Fluid Exposure Test:

[0080] A fifth procedural step seeks to determine whether or not theairbag module under investigation has been exposed to fluid (e.g. water)which may cause an undesirable degradation in module performance. Thisis achieved by visual inspection of the airbag module and through use ofAtomic Absorption Spectroscopy (AAS) techniques.

[0081] A motor vehicle may well become exposed to water during itsoperational life. Where a vehicle is partially or completely immersed inwater (for example, river, lake or sea water), perhaps as a result of aflood or a road traffic accident, it is possible for an installed airbagmodule to suffer water induced damage to the gas generator or the airbagitself. However, such damage may not be readily detected through asimple visual inspection.

[0082] The water most likely to be exposed to an airbag module (i.e.river, lake and sea water) characteristically contains detectable levelsof deposited metals such as calcium and sodium. Although an airbagmodule may be handled (and thereby inadvertently cleaned) followingexposure to water, a detectable level of calcium and/or sodium depositedon the module will tend to remain. The surface of the reaction canadjacent the gas generator is particularly likely to retain detectablecalcium/sodium deposits since this surface is covered by the airbag andis not therefore readily accessible either for unintentional orintentional cleaning. Through use of Atomic Absorption Spectroscopytechniques, a subject airbag module may be investigated for the presenceof positively charged cations associated with calcium/sodium. If thecalcium/sodium levels detected are greater than a predeterminedacceptable level, then it may be concluded that there is an unacceptablyhigh risk that the subject airbag module has suffered damage due toexposure to water.

[0083] Although any surface of an airbag module may be subjected to thefluid exposure test, it is highly preferable for the tested surface tobe one which not only readily receives and retains a fluid in which themodule is immersed, but a surface which is also unlikely to be wipedclean. Since the outer surfaces of a module may be cleaned quitereadily, it is preferable for the inner surface of reaction can adjacentthe gas generator to be investigated. Testing of this surface is alsodesirable since it is the gas generator which is most likely to sufferdamage from fluid exposure. Access to this surface may be gained throughapertures in the module. Disassembly of the module is not thereforenecessary.

[0084] Once a suitable surface for testing has been selected, a swab istaken from said surface using a wetting agent or more particularly asolvent such as 5% hydrochloric acid. The swab is taken from apredetermined magnitude of surface area. The swab is then reacted with a1% lanthanum chloride solution and the resulting solution analysed forlevels of calcium/sodium using Atomic Absorption Spectroscopy. A measureof calcium/sodium may be thereby derived in terms of milligrams perlitre (for a given magnitude of surface area). If considered necessary,the quantity of calcium/sodium detected on the tested surface (and thepredetermined level considered acceptable) may be expressed throughreference to a datum level. This may be achieved by analysing swabblanks (i.e. a solution of solvent (5% hydrochloric acid), which has notbeen applied to the test surface, and 1% lanthanum chloride solution)and subtracting the calcium/sodium levels thereof from those of a testsurface. Having determined the levels of calcium and sodium present onthe test surface, appropriate comparison of said levels with thepredetermined levels considered acceptable may then be made.

[0085] A number of factors should be considered when determining thecalcium/sodium levels above which there is an unacceptably high risk ofa subject airbag module having been exposed to water. Firstly, calciumdeposits will arise from fresh water sources such as rivers, ponds andlakes. Sodium deposits will arise from salt water sources. Atmosphericconditions (such as humidity) may also vary the calcium/sodium tracesfound on an airbag module. Thus, the place of manufacture and subsequentuse of an airbag module may give rise to heightened levels ofcalcium/sodium even though there has been no direct contact with waterwhich would be regarded as potentially damaging. Thus, the history of asubject airbag module (and that of the vehicle from which it has beenextracted) may well be relevant when undertaking the fluid exposuretest.

[0086] In addition to the visual and Atomic Absorption Spectroscopyinspection, the question of whether or not the airbag module has beenexposed to water is addressed by reference to the vehicle log (seeProcedural Step 1).

[0087] The electronic hardware controlling the investigation is adaptedto ask the operator for the module's identification number and toprovide the operator with appropriate instructions for conducting theAtomic Absorption Spectroscopy test. The identification number istypically supplied by scanning the bar code of the module'sidentification label. The electronic hardware also directs the operatorto undertake both a visual inspection of the subject module and a reviewof the associated vehicle log. On completion of the fluid exposure test,the controlling electronic hardware prompts the operator as follows —

[0088] Was evidence of fluid exposure detected?—Yes/No

[0089] If “No”, then completion of the fluid exposure test is confirmed.

[0090] If “Yes”, then the airbag module is rejected and not subjected tofurther investigation.

[0091] The results of the fluid exposure test are recorded under theidentification number of the subject module.

[0092] Procedural Step 6—Cosmetic Test:

[0093] A sixth procedural step seeks to determine whether an airbagmodule has been visually damaged to an extent which may potentiallydegrade module performance. This is achieved by visual inspection of theairbag module, with particular regard being had to the airbag cover andthe reaction can. The condition of any original paint orwarning/identification stickers on the subject module is alsoconsidered. If paint has been applied to the module since manufacture,then the module is rejected as unsuitable for future use. The electronichardware controlling the investigation is adapted to ask the operatorfor the module's identification number and to provide the operator withappropriate instructions for undertaking the cosmetic test. Theidentification number is typically supplied by scanning the bar code ofthe module's identification label. On completion of the cosmetic test,the controlling electronic hardware prompts the operator as follows —

[0094] Was any evidence of damage detected?—Yes/No

[0095] If “No”, then completion of the cosmetic test is confirmed.

[0096] If “Yes”, then the airbag module is rejected and not subjected tofurther investigation.

[0097] The results of the cosmetic test are recorded under theidentification number of the subject module.

[0098] If the airbag module under investigation is deemed to satisfy thecriteria set by the aforementioned procedural steps, then acertification label is prepared and attached to the reaction can (orother suitable component) of the module. The certification label statesthat the subject module is suitable for reinstallation by a qualifiedtechnician in a specified vehicle. Depending upon the type of gasgenerant used in the module, the certification will also indicate theexpiry date of the gas generator. Once the certification label has beensecurely attached, the airbag module is sealed within a tamper evidentcontainer. The airbag module is then suitable for re-sale and subsequentre-use.

[0099] The present invention is not limited to the specific methoddescribed above. Alternatives will be apparent to a reader skilled inthe art. For example, the procedural steps may be completed in an orderdifferent to that indicated hereinabove. It is, however, desirable forthe vehicle and airbag module details to be recorded before undertakingany tests. Further alternatives include the use of ICP (i.e. InductivelyCoupled Plasma), polarography or colourimetric techniques for the fluidexposure test rather than the Atomic Absorption Spectroscopy (AAS)technique discussed. When using these alternative techniques, a swab maybe taken from a subject airbag module in the manner described withregard to the Atomic Absorption Spectroscopy procedure.

1. A method of testing an airbag module comprising the step of testingsaid module for exposure to a given fluid.
 2. A method as claimed inclaim 1, wherein said given fluid is water.
 3. A method as claimed inclaim 1 or 2, wherein said fluid exposure test comprises the step ofinspecting said airbag module or a swab taken therefrom by means ofAtomic Absorption Spectroscopy techniques.
 4. A method as claimed in anypreceding claim, wherein said fluid exposure test comprises the step ofinspecting said airbag module or a swab taken therefrom for deposits ofa metal.
 5. A method as claimed in claim 4, wherein the step ofinspecting for deposits of a metal comprises the step of inspecting forcations.
 6. A method as claimed in claim 4 or 5, wherein the step ofinspecting for deposits of a metal quantifies the amount of metaldeposited.
 7. A method as claimed in claim 6, wherein the step ofinspecting for deposits of a metal quantifies the amount of metaldeposited for a given surface area of airbag module.
 8. A method asclaimed in any of claims 4 to 7, wherein the step of inspecting fordeposits of a metal comprises the step of taking a swab from a surfaceof said airbag module by applying a solvent to said surface.
 9. A methodas claimed in claim 8, wherein the solvent is 5% hydrochloric acid. 10.A method as claimed in claim 8 or 9, wherein the step of inspecting fordeposits of a metal further comprises the step of agitating said swabwith 1% lanthanum chloride solution.
 11. A method as claimed in claim10, wherein the step of inspecting for deposits of a metal furthercomprises the step of inspecting the mixture of 1% lanthanum chloridesolution and swab by means of Atomic Absorption Spectroscopy so as todetermine the quantity of a deposited metal present in said mixture. 12.A method as claimed in any of claims 8 to 11, wherein said swab is takenfrom a surface of said airbag module which cannot be conveniently wipedclean.
 13. A method as claimed in claim 12, wherein said surface is asurface of or adjacent a gas generator of said airbag module.
 14. Amethod as claimed in claim 12, wherein said surface is a surface of areaction can of said airbag module.
 15. A method as claimed in any ofclaims 4 to 14, wherein the fluid exposure test comprises the furtherstep of determining a threshold quantity of a deposited metal which, iffound on said airbag module, indicates an unacceptable risk of saidmodule having been damaged through fluid exposure.
 16. A method asclaimed in any of claims 4 to 15, wherein said deposited metal iscalcium or sodium.
 17. A method as claimed in claim 1 or 2, wherein saidfluid exposure test comprises the step of inspecting said airbag moduleor a swab taken therefrom by means of Inductively Coupled Plasma,polarography or colourimetric techniques.
 18. A method of testing anairbag module comprising the steps of: (i) locating an airbag modulewhich has been previously installed; (ii) establishing a set of criteriato be satisfied before said airbag module is deemed acceptable forfuture use; and (iii) investigating against said set of criteria so asto determine the acceptability of said airbag module for future use. 19.A method as claimed in claim 18 comprising the methods of testing anairbag module for exposure to a given fluid according to any of claims 1to 17.